The epidermal stratum corneum is responsible for providing a barrier function for preventing evaporation of moisture from the body and irritation or penetration by foreign matter from the exterior. The stratum corneum is constituted of corneocytes and intercellular lipids, and the corneocytes are enclosed within a cell membrane-like structure called the cornified envelope. The cornified envelope helps to establish a stable corneocyte structure and is an important structure for maintaining the skin barrier function. The cornified envelope is formed by cornification of keratinocytes in a basal layer of the horny cell layer and synthesis of involucrin (also referred to as “IVL” herein), loricrin other proteins necessary for cornification, whereafter the proteins are crosslinked by activation of transglutaminase. Expression and synthesis of the involucrin and activation of the transglutaminase are important for normal formation of the cornified envelope and normal epidermal cornification, and also for maintenance and improvement of the skin moisturizing function. In this respect, involucrin expression enhancement and transglutaminase activation are reported to lead to normal skin cornification, improvement of the barrier function and improvement of skin roughness (see, for example, Non-Patent Literatures 1 and 2, and Patent Literatures 1 and 2).
Moreover, ceramides, which are one class of sphingolipids, are lipids present only in an extremely small amount relative to the whole organism. However, in the stratum corneum which is the outermost layer of the skin, the content of ceramides is more than half that of lipids, and these ceramides play important roles in the moisturizing function and barrier function of the skin. These ceramides are produced in the epidermal cells, then secreted to form a lamellar structure in intercellular spaces of the stratum corneum, and they maintain the stratum corneum functions. It has been extensively reported that, in skin diseases such as dry skin, rough skin, atopic dermatitis, senile xerosis and psoriasis, normal metabolism of ceramides is inhibited and the amount of ceramides in the stratum corneum decreases, which leads to deterioration of moisturizing function, incomplete epidermal cornification, and decline in the barrier and other functions of the skin (see Non-Patent Literature 3). It is thought that a substance which enhances production of ceramides would have effects such as animal cell proliferation inhibition, differentiation induction, and apoptosis induction, and furthermore could be expected to have therapeutic effects on diseases due to cell proliferation or abnormal differentiation, such as inflammatory diseases and malignant tumors (see Non-Patent Literature 4). Moreover, it has been reported that ceramides have an effect of inhibiting bone resorption, an effect of strengthening bone, and an effect of inhibiting decrease in alveolar bone, and are useful for preventing and ameliorating bone and joint diseases such as osteoporosis, bone fracture, low back pain, and rheumatism (see Patent Literature 3), that ceramides have an effect of preventing or reducing periodontal diseases (see Patent Literature 4), and that ceramides have an effect of imparting bounce and resilience to the hair and an effect of improving the feel of the hair (see Patent Literature 5).
Thus, various efficacies can be expected from ceramides, and thus an effort to discover substances that can enhance ceramide production is desirable.
Moreover, cornification-related proteins such as involucrin are known to also play a role in hair growth. For example, it has been reported based on the result of gene expression analysis in the hair root that involucrin gene expression is significantly higher in persons with wavy hair, and that a substance that increases involucrin gene expression can act as a wavy hair or curly hair promoter or a wave formation enhancer (see Patent Literature 6).
On the other hand, the plants of family Acanthaceae contain about 250 genera and 2,500 species. Of these plants, those in the genus Justicia are believed to include about 300 species. Particularly noteworthy is that Justicia procumbens has been used as a Chinese medicine, for example, to treat arthritic pain and reduce fever, and that Justicia gendarussa, a plant in the same genus Justicia, is known as an ingredient of a skin analgesic for external application and a skin anti-itching agent for external application (see, for example, Patent Literatures 7 and 8). Moreover, Adhatoda vasica, a plant in a different genus in the same family Acanthaceae, is known to have a ceramide production enhancing effect (for example, Patent Literature 9). Further, physiological activities of an extract from Justicia procumbens are known to include a melanin formation inhibiting effect and a dopa oxidase activity inhibiting effect (for example, see Patent Literature 10).
However, the extract from Justicia procumbens has not up to now been known to activate transglutaminase and enhance ceramide production, or to be useful for maintaining or improving skin barrier function or moisturizing function, or preventing or improving skin roughness.
Moreover, an extract from Peristrophe japonica, a plant belonging to the family Acanthaceae, genus Peristrophe, is known to exhibit physiological activities including a melanin formation inhibiting effect, a dopa oxidase activity inhibiting effect, and the like (for example, see Patent Literature 11). However, the extract from Peristrophe japonica has not so far been known to activate transglutaminase and enhance ceramide production and involucrin expression, or to be useful for maintaining or improving skin barrier function or moisturizing function, or preventing or improving skin roughness, or forming wavy hair, curly hair, or wave formation.
Further, arylnaphthalene lignans are known to be isolatable from an extract from plants such as Haplophyllum patavinum and Cleistanthus collinus (see, for example, Non-Patent Literatures 5 and 6). Physiological activities of the arylnaphthalene lignans are known to include a bone resorption inhibiting effect, and a cell differentiation inducing factor reinforcing effect on osteoblasts and neurons (see, for example, Patent Literatures 12 and 13). Further, Justicidin A, Justicidin B, Diphyllin and Tuberculatin are known to have antiviral activity or antitumor activity (see, for example, Non-Patent Literatures 7 and 8). Furthermore, Justicidin A and Cleistanthin A are known to have antitumor activity (see, for example, Non-Patent Literatures 9 and 10, and Patent Literature 14), and a melanin formation inhibiting effect and a dopa oxidase activity inhibiting effect (for example, see Patent Literature 11), and the like. However, arylnaphthalene lignans represented by Formula (1) as set out below have not so far been known to activate transglutaminase and enhance the ceramide production and the involucrin expression, or to be useful for maintaining or improving the skin barrier function or moisturizing function, or preventing or improving skin roughness, and forming wavy hair or curly hair or wave formation.